A multimedia broadcast multicast service (MBMS, Multimedia Broadcast Multicast Service) is one of the important contents in the development of the Third Generation Partnership Project (3GPP) services. In the MBMS, the network can send the same multimedia data to multiple mobile terminals on the network in broadcast or multicast mode. Compared with a single user transmission mode, the MBMS greatly saves air interface resources of a system. According to the long-term evolution (LTE) MBMS R9 protocols formulated recently, an MBMS service is transmitted over a multimedia broadcast multicast service single frequency network (MBSFN, Multimedia Broadcast multicast service Single Frequency Network). In MBMS transmission mode, an MBMS service is transmitted synchronously at the same frequency in multiple cells at the same time. This transmission mode effectively saves frequency resources, improves spectrum usage rate, and enhance coverage rate.
FIG. 1 illustrates a logical architecture of an MBMS at the side of E-UTRA. MBMS service control signaling is transmitted by an MME (mobility management entity) to eNB through M3 and M2 interfaces, to set up MBMS service sessions and allocate resources synchronously. MBMS service user plane data is transmitted by an MBMS GW (gateway) to the eNB through an M1 interface, and synchronous transmission of the user plane data is implemented over the sync protocol (synchronization protocol).
A multi-cell/multicast coordination entity (MCE, multi-cell/multicast coordination entity) is a logical entity, and can be configured with multiple MBSFN areas (MBSFN Area) used for MBSFN transmissions, and can allocate radio resources to all evolved Node Bs (eNB, evolved Node B) for multi-cell transmissions in the MBSFN areas. One MBSFN area may include multiple eNBs (multiple cells). All cells in the same MBSFN area broadcast the same contents in synchronous mode. Each MBMS service is broadcast in a specific service area (Service Area), and one service area may include multiple MBSFN areas, that is, multiple cells.
The process of broadcasting an MBMS service is as follows: Before the MBMS service is broadcast on the air interface (may be several hours earlier), a UE (user equipment) receives a service description from the application layer, where the service description includes a list of MBMS services to be broadcast and service start time. Before the services are formally broadcast (a duration of several seconds), a cell broadcasts an MCCH (Multicast Control Channel, multicast control channel) change notification (change notification) in a PDCCH (physical downlink control channel, physical downlink control channel) channel. Configuration information about the time of sending the notification is broadcast in a SIB (system information block, system information block) 13. The UE monitors the PDCCH according to the configuration information in the SIB 13; and when reading the MCCH change notification (change notification), the UE reads control information of an MBMS service from the MCCH, and learns which service starts to be broadcast.
For the UE, if the UE is receiving an MBMS service or is interested in an MBMS service, best efforts should be made to ensure that the UE camps on a cell that can provide the corresponding service, so that users can enjoy a better experience.
Therefore, in the prior art, a UE in an idle state that is receiving an MBMS service and is interested in an MBMS service sets the priority of the frequency of the MBMS to the highest, that is, the UE gives a top priority the frequency of the MBMS cell in the case of cell reselection.